Agricultural tractors are fitted at the front and/or at the rear with a hitch, also termed a hydraulic power lift, for attachment of towed implements, such as ploughs or harrows. A three-point hitch comprises two hydraulically powered lower lifting arms, and an upper arm, also termed a top link, positioned above and centrally between the lifting arms. Each lifting arm commonly forms part of a parallelogram-like lever system comprising mutually pivoted links of which an upper link is connected to a hydraulic cylinder, to allow the lower arm to be raised and lowered. In the case of a front hitch, each lifting arm of the hitch may additionally be pivotably connected to the lower link so that it may be moved manually between a deployed position and a parked position. In this case, the lifting arm is retained in one of these two positions by means of locking pin that passing through holes in the lower link and the lifting arm.
At its free end, each of the three arms of the hitch has a coupling element in the form an upwardly facing part-spherical socket for receiving a coupling ball and a latch for retaining the coupling ball within the socket. The ball has a through bore to receive a coupling pin on the implement being towed. The ball and socket together avoid the hitch arms and implement coupling pins from being stressed when the towed implement is not precisely aligned with the tractor.
Coupling balls come in different shapes and sizes and are selected to suit the implement to be towed by the tractor. In particular, the size of the coupling pins will vary between implements and the outer diameter of the coupling balls may vary between the lifting arms and the top link. Furthermore, different variants of coupling balls exist, for example with and without cylindrical shoulders on the opposite sides of the through bore. As a result of this, a tractor is required to carry several coupling balls to suit all eventualities and these balls need to be stored in a convenient manner because they cannot be left on the arms of the hitch, nor can they be left on the towed implement.
Conventionally, the coupling balls have been kept in a toolbox, stored near the cab entrance. The disadvantage of storing coupling balls in this manner is that they are far removed from the hitch and the operator has to keep moving from the hitch to the toolbox to collect or replace the coupling balls one at a time.
This problem has been addressed in EP 1795060, which is believed to represent the closest prior art of the present invention. The solution proposed EP 1795060 is to provide a holder that can be mounted near the hitch, the holder comprising a rear wall, two side walls and an open upper end, the side walls retaining the balls within the holder with the inside surfaces of the side wall in contact with portions of the spherical surfaces of the balls which face away from the rear wall, and bias means for biasing the balls into contact with the inside surfaces of the side walls.